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Geology Site Account

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Orsett Cock Quarry, ORSETT, Thurrock District, TQ65588115, Potential Local Geological Site

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Site name: Orsett Cock Quarry

Grid reference: TQ 6558 8115

Brief description of site:

Site of geological interest with exposures of the pebble beds of the Upnor Formation (formerly called the Woolwich Bottom Bed). Although the area currently exposed is very small, it is still the best inland exposure of this particular formation. The quarry is private land and access is only available with the prior permission of the land-owner.

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Summary of geological interest

Also known as Southfields quarry, the private quarry behind the old Orsett Cock public house provides a fine exposure of the basal part of the Upnor Formation. Formerly called the Woolwich Bottom Bed it rests on the Thanet Sand (not currently visible in this pit) and consists almost entirely of well-rounded, often almost spherical, pebbles representing a cross section through an ancient subtropical sea floor some 55 million years old

The strata, almost 9 metres thick, consists almost entirely of pebbles, with occasional layers of sand and dips 21 degrees to the east. The pebbles are black, with a pale grey interior, and many have crescent-shaped percussion or ‘chatter-marks’, indicating that they have been pounded together on a beach or just offshore in a high energy environment. This bank of pebbles was an impressive sight forming a self supporting vertical cliff. The deposits, formerly thought to be Blackheath Beds, were probably part of an offshore barrier in fairly shallow water.

There are two fine colour photographs of the section here in the geological survey memoir for the London area (Ellison 2004). It is therefore important to obtain preservation of one of these faces in any reclamation scheme, particularly as the important Orsett Depot Pit to the south has now been infilled.



Shallow marine pebble beds of the Upnor Formation at Orsett. Photo © British Geological Survey (P211788).

 

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